1Discard any broken-shell or open (dead) clams. Place remaining clams in large container. Cover with water and vinegar; let stand 30 minutes; drain. Scrub clams in cold water.
2Cook onion, broth, wine, tomato paste, oregano, fennel seed, saffron, red pepper and tomatoes in Dutch oven over medium heat about 10 minutes, stirring occasionally, until onion is tender.
3Stir in clams and fish. Cover and cook 5 minutes. Stir in rice. Cover and cook about 3 minutes, removing clams as they open, until all clams have opened. Discard any unopened clams. Return clams to stew. Mix parsley and lemon peel; sprinkle over stew.